System and method for clamping a chassis cover

ABSTRACT

A system is provided for securing a cover having a first surface onto a chassis having a rim, the rim having a second surface. The system comprises a clamping rail and a fastener coupled to the rail. The clamping rail is configured to form a loop that circumferentially engages the first surface and the second surface and, when constricted, produces a first force substantially coplanar with the loop. The fastener is configured to constrict the rail, the rail and the first and second surfaces configured to produce a second force having a component substantially orthogonal to the loop when the rail is constricted.

TECHNICAL FIELD

The present invention generally relates to clamps, and more particularly relates to a system for clamping a cover to a power electronic bay chassis.

BACKGROUND OF THE INVENTION

In recent years, advances in technology have led to substantial changes in the design of automobiles. One of the principal changes involves the complexity, as well as the power usage, of various electrical systems within automobiles, particularly alternative fuel vehicles. During this time, the requirement for electrical power generation in automotive applications has risen dramatically. This trend had been in place for decades but has accelerated in the last few years largely due to the advent of hybrid, electric, and fuel cell based vehicles. Such vehicles often use electrochemical power sources, such as batteries, ultracapacitors, and fuel cells, to power the electric motors that drive the wheels, sometimes in addition to another power source, such as an internal combustion engine.

In hybrid and fuel cell vehicles, a Power Electronics Bay (PEB) performs many necessary functions related to power conversion and distribution. PEB enclosures or chassis are typically designed to provide housed components with both environmental protection and shielding from incoming and outgoing electromagnetic interference (EMI). A PEB chassis generally comprises a body and cover constructed of either stainless steel or aluminum, each member having a machined sealing flange along an outer edge, pre-drilled to accommodate fastening bolts. One or both of the flanges typically has a groove to support a metal-impregnated, conductive, silicone o-ring to form an environmental seal when the cover of the enclosure is bolted closed. EMI shielding is provided by the continuous conductive shrouding formed by the metallic structure of the body and cover in conjunction with the conductivity of the o-ring in the seam. Because strong and evenly distributed clamping pressure is needed to provide a reliable seal, reinforcement of sealing flanges is typically required to provide adequate rigidity and prevent warping from the substantial compressive forces generated by a plurality of bolts spaced 1″ to 2″ apart. As a result, part count and overall vehicle weight are increased along with the complexity of associated assembly processes. Further, conductive, EMI shielding o-rings are often nickel-filled and add additional expense while contributing no additional environmental protection compared to conventional, non-conducting silicone rubber o-rings.

Accordingly, it is desirable to provide a system for clamping a cover to a PEB chassis that is easily installable and eliminates the need for multiple fasteners. Further, it is desirable that such a system provides EMI shielding along the seams and corners of a PEB chassis without the use of a conductive o-ring. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.

SUMMARY OF THE INVENTION

A system is provided for securing a cover having a first surface onto a chassis having a rim, the rim having a second surface. The system comprises a clamping rail and a fastener coupled to the rail. The clamping rail is configured to form a loop that circumferentially engages the first surface and the second surface and, when constricted, produces a first force substantially coplanar with the loop. The fastener is configured to constrict the rail, the rail and the first and second surfaces configured to produce a second force having a component substantially orthogonal to the loop when the rail is constricted.

A method is provided for clamping a cover having a first surface onto a chassis body having a rim, the rim having a second surface. The method comprises the steps of circumferentially aligning a clamping rail to the first and second surfaces, constricting the circumference of the clamping loop to engage the first and second surfaces with a first force substantially coplanar with the loop, the clamping loop and the first and second surfaces being configured to convert at least a portion of the first force to a second force substantially orthogonal to the loop that clamps the cover onto the rim, and fixing the clamping loop in its circumferentially restricted position.

DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and

FIG. 1 is a schematic view of an exemplary automobile illustrating the manner in which an embodiment is integrated with various sub-components of an automobile;

FIG. 2 is an isometric view of a power electronics bay enclosure in accordance with a first embodiment of the present invention;

FIGS. 3-5 are cross-sectional schematic drawings illustrating clamping rails in accordance with further embodiments of the present invention;

FIGS. 6-7 are isometric views of a clamping rail in accordance with a further embodiment of the present invention;

FIG. 8 is an isometric view of a clamping rail and corner brace in accordance with yet a further embodiment of the present invention;

FIGS. 9-10 are isometric views of a clamping rail and fastener in accordance with yet a further embodiment of the present invention;

FIG. 11 is an isometric view of a clamping rail integrated with a lever-actuated fastener in accordance with yet a further embodiment of the present invention;

FIG. 12 is an isometric view of a clamping rail corner structure in accordance with yet a further embodiment of the present invention; and

FIG. 13 is an isometric view of a clamping rail welded in accordance with yet a further embodiment of the present invention.

DESCRIPTION OF AN EXEMPLARY EMBODIMENT

FIG. 1 illustrates a vehicle 10, (e.g. an automobile), according to one embodiment of the present invention. The automobile 10 includes a chassis 12, a body 14, four wheels 16, and an electronic control system (or electronic control unit (ECU)) 18. The body 14 is arranged on the chassis 12 and substantially encloses the other components of the automobile 10. The body 14 and the chassis 12 may jointly form a frame. The wheels 16 are each rotationally coupled to the chassis 12 near a respective corner of the body 14.

The automobile 10 may be any one of a number of different types of automobiles, such as, for example, a sedan, a wagon, a truck, or a sport utility vehicle (SUV), and may be two-wheel drive (2WD) (i.e., rear-wheel drive or front-wheel drive), four-wheel drive (4WD), or all-wheel drive (AWD). The automobile 10 may also incorporate any one of, or combination of, a number of different types of engines (or actuators), such as, for example, a gasoline or diesel fueled combustion engine, a “flex fuel vehicle” (FFV) engine (i.e., using a mixture of gasoline and alcohol), a gaseous compound (e.g., hydrogen and/or natural gas) fueled engine, or a fuel cell, a combustion/electric motor hybrid engine, and an electric motor.

In the exemplary embodiment illustrated in FIG. 1, the automobile 10 is a fuel cell vehicle, and further includes an actuator assembly (or powertrain) 20, a battery 22, a battery state of charge (SOC) system 24, a power electronics bay (PEB) 26, and a radiator 28. The actuator assembly 20 includes an internal combustion engine 30 and an electric motor/generator (or motor) system (or assembly) 32. The battery 22 is electrically coupled to the PEB 26 and, in one embodiment, comprises a lithium ion (Li-ion) battery including a plurality of cells, as is commonly understood. PEB 26 is typically comprised of a plurality of electronic components, including those operating with high voltage, enclosed in a housing or chassis that provides protection from both environmental damage and shielding for incoming and outgoing EMI.

FIG. 2 illustrates an exemplary PEB chassis 120 that houses electronic components in accordance with a first exemplary embodiment. These components may include a DC/DC converter 122 to boost fuel cell DC voltage to a higher voltage, a DC/AC inverter 124 for delivering AC power to a primary electric drive motor, an additional DC/AC inverter 126 to deliver power to a compressor, a set of boost inductors 130 to boost fuel cell output voltage as part of the boost converter, and one or more circuit boards 132 containing support electronics for a myriad of functions. PEB chassis 120 has a body 144 comprised of a rectangular bottom panel 146, four side panels 148 interconnected together, and a removable top or cover panel 152. Body 144 is typically constructed from a conductive and corrosion resistant material such as rolled stainless steel sheets welded at side and bottom seams, or from a die-cast and anodized aluminum alloy. Likewise, cover 152 is also constructed of stamped sheet metal or a cast aluminum alloy, and is fabricated to fit over the top of body 144. Any of the side/top/bottom panels of chassis 120 may be specifically configured to include contours and/or openings such as port 153 to accommodate internal components housed therein, and/or provide a means of interconnection to other components of vehicle 10. While FIG. 2 illustrates PEB chassis 120 as a rectangular prism, it should be understood that other shapes may be used depending on the space and size constraints of the application and the type and size of components to be housed. Further, while FIG. 2 illustrates only clamping for a cover panel, it should be understood that any non-integrally connected side and/or bottom panel may also be clamped.

Referring to FIG. 2, a clamp 160 comprises a continuous rail 164 having first and second ends 172 and 173 respectively, coupled together by an adjustable fastener 156 to form a clamping loop 150. Fastener 156 may be used to precisely contract or expand the circumference of clamp 160 to a desired circumference by providing a means to controllably adjust the distance between first and second ends 172 and 173. Prior to clamping, fastener 156 may be loosened to expand the circumference of clamp 160 and facilitate alignment to clamping surfaces of cover 152 and sidewalls 148. When clamped, rail 164 conformably circumscribes these surfaces and applies constrictive forces about cover 152 and sidewalls 148 that are substantially coplanar with clamping loop 150. As will be described in greater detail below, rail 164 is configured to engage with cover 152 and sidewalls 148 and apply clamping pressure thereto by converting the coplanar forces to clamping forces having a component substantially orthogonal to loop 150.

FIG. 3 illustrates a cross sectional schematic drawing of cover 152 aligned over sidewall 148 and proximate to clamping rail 164 prior to clamping in accordance with an exemplary embodiment. The upper edge of sidewall 148 comprises an integrally formed rim 168 having a surface 198 machined to engage a flat machined undersurface 200 of cover 152. A groove 192 is formed in rim 168 and runs along its length, and a seal 188 sized somewhat larger than the width and depth of groove 192, is disposed therein. Types of seals that may be used include but are not limited to o-rings, gaskets, or curable liquids/gels. Alternatively, undersurface 200 may be configured to receive a seal, or both rim surface 198 and undersurface 200 may each be grooved to accommodate a seal.

Prior to clamping, cover 152 rests on the top of seal 188 forming a gap 218 between undersurface 200 and rim surface 198. The underside of rim 168 comprises a rim bevel 216 that extends outward from sidewall 148 terminating with a vertical rim lip 176. The top peripheral surface of cover 152 has an edge bevel 214 terminated by a short vertical cover lip 190. Rail 164 is configured to fit over edge bevel 214 and rim bevel 216 when clamped and comprises a center section 208 that couples together upper and lower arms 202 and 204 respectively. Each arm may terminate with an outwardly curving upper and lower leading edge 206 and 226 respectively, to facilitate aligning rail 164 with rim 168 and cover 152 prior to clamping. While rail 164 has been illustrated as having angled, symmetric upper and lower arms 202 and 204, it should be understood that arms may be asymmetric with respect to angle and/or length. For example, as illustrated in FIG. 4, cover edge bevel 214 and rim bevel 216 differ with each other with respect to both length and bevel angle. Similarly, upper arm 202 and lower arm 204 of rail 164 differ in length and in angle from center section 208. In general, rail 164 imparts a clamping force that clamps cover 152 to rim 168 when the plane of upper arm 202 is different than the plane of cover edge bevel 214, and/or the plane of lower arm 204 is different than the plane of rim bevel 216.

FIG. 5 illustrates a cross sectional schematic drawing of cover 152, rim 168, and rail 164 in a closed and clamped position in accordance with the exemplary embodiment. Rail 164 has been moved into a clamping position by a force (depicted by arrow F1) substantially coplanar with loop 150 and generated by, for example, tightening fastener 158 (FIG. 2) to decrease the circumference of clamp 160. As the circumference is decreased, F1 increases and upper and lower arms 202 and 204 are pulled (inward toward the center of loop 150) onto edge and rim bevels 214 and 216 causing rail 164 to deform conformably to these bevels. When deformed, rail 164 responds in a springlike manner and generates forces comprising opposing (clamping) components, F1 and F2, substantially orthogonal to the plane of loop 150 that are applied to edge and rim bevels 214 and 216, and press cover 152 onto rim 168. Clamping forces F2 and F3 may be increased by further tightening of fastener 158 until either the spring force decreases due, for example, to rail 164 yielding in plastic deformation or until center section 208 abuts against rim lip 176 and/or cover lip 190. As clamping pressure increases, seal 188 is compressed in conformity with cover 152 and groove 192 to create a tight environmental seal. Clamping forces F2 and F3 may be controlled by a proper adjustment of fastener 158 to retain a narrow gap 218, and avoid permanent deformation or scarring of undersurface 200 and/or top surface 198 thereby. As is well known by those with skill in the art, available clamping forces can be adjusted by design factors that include but are not limited to the angle and/or lengths of edge and rim bevels 214 and 216, the angle and/or length of the upper and lower rail arms 202 and 204, the spring constant of rail 164, and the applied force F1.

Rail 164 provides EMI shielding over gap 218 all along its length including around chassis corners as will be described in further detail below. Such shielding results from factors that include the metallic construction and shape of rail 164, and reduces the amount of EMI passing between rim 168 and cover 152 from sources either internal or external to a chassis. Center section 208 of rail 164 may be configured to be substantially perpendicular to gap 218 to provide improved coverage and greater attenuation of such EMI signals.

FIG. 6 illustrates an isometric view of a clamp 240 in accordance with another exemplary embodiment. Clamp 240 is configured for a rectangular chassis and comprises a first and second L-shaped section of clamping rail 236 and 238 respectively, each rail having a cross-sectional geometry suitable for clamping in accordance with this invention such as that depicted for rail 164 in FIG. 3. A first backing strap 230 is mounted to first rail 236 in a parallel fashion, and traverses conformably along its entire length. A second backing strap 232 is likewise conformably mounted parallel to second rail 238. Each strap 230 and 232 is comprised of a rolled carbon steel or stainless steel alloy sheet attached to its respective rail using rivets, spot-welds, or the like. First and second rails 236 and 238 are coupled together to form a rectangular loop using first and second fasteners 246 and 248 respectively. Fasteners 246 and 248 are each configured to be tightened or loosened to adjust the peripheral distance spanned by clamp 240. Prior to clamping, fasteners 246 and 248 may be loosened to expand the peripheral distance and facilitate mounting and alignment of clamp 240 to the rim and cover of a chassis. Following alignment, clamp 240 may be constricted by tightening fasteners 246 and/or 248 to generate a clamping force. While clamp 240 has been shown having two opposing corner fasteners, those having skill in the art will appreciate that clamp 240 may be configured with a single corner fastener or with more than two corner fasteners depending upon space and/or other overall design considerations.

FIG. 7 illustrates the interaction of first and second backing straps 230 and 232 with fastener 246 disposed at a corner of clamp 240 in accord with an exemplary embodiment. Fastener 246 is comprised of a t-bolt 262 having a fixed head 250, and slidably coupled to a crosstie 260. In one embodiment, t-bolt 262 is bent to more conformably accommodate a corner. Crosstie 260 may slide in either direction along t-bolt 262 and is bounded between a nut assembly 254 and head 250. Nut assembly 254 is threadably coupled to t-bolt 262 and, when tightened, forces second crosstie 260 controllably toward head 250. First backing strap 230 is divided at its end and forms a pair of loops 265 each rotatably coupled to an end of head 250 forming a first hinge 269. Second backing strap 232 is similarly split to form a second hinge 271 rotatably coupled to the ends of second crosstie 260. The hinged coupling of fastener 246 to backing straps 230 and 232 allows clamp 240 to adjust more conformably and apply pressure more evenly in chassis corners. Prior to clamping, nut assembly 254 may be loosened to allow separation of head 250 and crosstie 260, and expansion of clamp 240 thereby. To apply clamping pressure, nut assembly 254 may be tightened to force head 250 and crosstie 260 toward each other, constricting clamp 240 thereby.

FIG. 8 is an isometric view of a fastening assembly 298 configured for clamping a chassis corner in accordance with an exemplary embodiment. First and second clamping rails 300 and 302 may represent end segments of longer rail sections of a clamp 296 fabricated for a rectangular chassis. First rail segment 300 and second rail segment 302 have first and second bent ends 304 and 306 respectively, contoured to conformably engage with a first and second corner brace 308 and 3 10. An adjustable fastener 320 is comprised of first and second crossties 322 and 324, respectively, that slidably engage first and second corner braces 308 and 310 along a threaded rod 312. A nut 318 threadably coupled to a first end 321 of rod 312 may be rotated to adjust the distance between the crossties and braces, and by their engagement, to adjust the distance between first and second bent ends 304 and 306 respectively. Prior to clamping, clamp 296 may be expanded to facilitate alignment to a chassis cover/rim by loosening nut 318. Clamp 296 may be constricted to apply clamping pressure using nut 318 to adjust the distance between first and second braces 308 and 310 and thus also first and second bent ends 304 and 306.

FIG. 9 is an isometric view of a clamp assembly 270 in accordance with another exemplary embodiment. Clamp assembly 270 is configured for a rectangular chassis and comprises first and second rails 276 and 278, respectively, each rail formed in the shape of an asymmetric U having two right angle bends. Rails 276 and 278 are coupled together along straight rail sections by a first and second adjustable fastener 272 and 274. As in previous embodiments, one or both of fasteners 272 and 274 may adjust the circumference of clamp 270 by loosening for alignment or removal, or by tightening to apply clamping as required. An isometric side view of an exemplary fastener 272 in accordance with this embodiment is illustrated in FIG. 10. Fastener 272 is configured in a similar manner to fastener 246 shown in FIG. 7, and comprises a threaded rod 280 coupled to a first crosstie 282 at a first end 293, and slidably coupled to a second crosstie 288 and a hollow sleeve 284. First crosstie 282 is rotatably coupled to a first backing loop 290 to form a first hinge 294, and second crosstie 288 is likewise rotatably coupled with a second backing loop 292 to form a second hinge 295. Backing loops 290 and 292 are each attached to ends of rails 276 and 278 respectively in a well-known manner using a rivet or weld. A nut 286 may be rotated to move sleeve 284 along rod 280 and adjust the distance between first and second crossties 282 and 288. Fastener 272 may thus be loosened to expand clamp 270 to facilitate alignment to or removal from a chassis, or tightened to contract the circumference of clamp 270 to apply clamping pressure.

FIG. 11 is an isometric side view of a lever-actuated fastener 360 used to couple together first and second clamping rails 362 and 364, respectively, forming a clamp 361 in accordance with a further embodiment. Fastener 360 comprises a lever 368 having a first end 380 configured with an angled leading edge 384 to facilitate actuation by a user. Lever 368 has a second end 382 rotatably hinged to a first base 378 by a pin 366. First base 378 is attached to first rail 362 using rivets, spot-welds, or the like. A second base 374, having an upwardly curved catch 372, is mounted to second rail 364 similarly using rivets, spot-welds, or the like. A U-shaped latch 370 straddles lever 368 and has first and second (not shown) hooked ends 376 and 377, respectively, that are rotatably coupled either side of lever 368 via openings therein. Latch 370 comprises a loop 373 configured to engage catch 372 when in a locked position and is free to swing about lever 368 when not engaged. Prior to clamping, lever 368 is rotated about pin 366 clockwise (as shown) to an unlocking position by applying an upward force to the underside of leading edge 384. In the unlocking position, latch 370 moves toward and disengages from catch 372, enabling adjustment of first and second rails 362 and 364 to allow clamp 361 to be aligned to or removed from a chassis. Fastener 360 is brought into a locking position by first engaging loop 373 with catch 372, followed by rotating lever 368 into a locked position over first base 378 (as shown). When fastener 360 is in the locked position, the resulting circumference of clamp 361 is fixed and depends on the lengths of first and second rails 362 and 364 as well as on the placement and dimensions of fastener 360. Achieving a desired circumference that will result in a desired clamping pressure therefore requires precise placement and sizing of these components.

FIG. 12 illustrates an isometric side view of a clamping rail 350 configured to conform to a chassis corner in accordance with an exemplary embodiment. Rail 350 has a cross section similar to that of rail 164 shown in FIG. 3 and comprises an upper and lower arm 340 and 342 respectively, coupled to a center section 338. Portions of upper arm 340 and lower arm 342 are removed in the region of rail 350 adjacent to a chassis corner to form upper and lower notches 332 and 334, respectively, and a center bridge 336 thereby. Those having skill in the art will appreciate that the depth, width, and/or shape of notches 332 and 334 may be varied provided that bending rail 350 to accommodate a corner does not result in deformation and/or structural damage to arms 340 and 342 or bridge 336. Notching of rail 350 may reduce clamping pressure somewhat in corners. This condition may be mitigated by minimizing the width of notches 332 and 334 and/or by designing the cover and rim to have greater rigidity in corner regions. EMI shielding remains continuous in chassis corners due to the continuity of bridge section 336 overlying the cover/rim seam around such corners.

FIG. 13 illustrates an isometric view of a clamp 390 having a circumference fixed by a weld in accordance with an exemplary embodiment. Clamp 390 is configured for a rectangular chassis and comprises a single clamping rail 394 having four right angle bends, each bend configured with corner notches 396 as depicted in FIG. 12 and previously described. Rail 394 is fabricated from a weldable material such as a carbon or stainless steel and has first and second ends 398 and 400, respectively, pre-cut to a circumference compatible with a chassis to be clamped. Prior to clamping, first and second ends 398 and 400 may be freely adjusted to align rail 394 to the chassis cover/rim. After alignment, first and second ends 398 and 400 are forced together using an appropriate means to constrict the circumference of clamp 390, and joined with a weld 392. In further embodiments, first and second ends 398 and 400 may be riveted, clasped, or crimped together. When joined using any of these methods, the circumference of clamp 390 is fixed and applies a corresponding clamping pressure to the chassis cover/rim. Fixing rail 394 in this manner may be used when access to the interior of the chassis for periodic maintenance of its contents is deemed unnecessary.

While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof. 

1. A system for securing a cover having a first surface onto a chassis having a rim, the rim having a second surface, the system comprising: a clamping rail configured to form a loop that circumferentially engages the first surface and the second surface and, when constricted, produces a first force substantially coplanar with the loop; and a fastener coupled to the rail configured to constrict the rail, the rail and the first and second surfaces configured to produce a second force having a component substantially orthogonal to the loop when the rail is constricted.
 2. A system according to claim 1, wherein the fastener further comprises a threaded rod coupled to the rail, the threaded rod configured to adjustably constrict the rail.
 3. A system according to claim 1, wherein the fastener further comprises a lever rotatably coupled to the rail and having a closed position, the lever configured to constrict the rail when the lever is actuated into the closed position.
 4. A system according to claim 1, wherein the fastener is rotatably coupled to the clamping rail.
 5. A system according to claim 1, wherein the clamping rail is coupled to a backing strap.
 6. A system according to claim 1, wherein the fastener is coupled to a backing strap.
 7. A system according to claim 1, wherein the clamping rail further comprises an upper arm that engages the first surface and a lower arm that engages the second surface.
 8. A system according to claim 7, wherein the upper and lower arms have different lengths.
 9. A system according to claim 7, wherein the rim further comprises a corner and the upper and lower arms of the rail are notched proximate to the corner.
 10. A system according to claim 1, wherein the rail further comprises corner braces, and wherein the fastener is coupled to the corner braces and is configured to constrict the rail by adjusting the corner braces.
 11. A system according to claim 1, wherein at least one of the rim and the cover further comprises a groove, and further comprising a seal that engages the groove and seals the chassis when the cover is clamped onto the rim.
 12. A system according to claim 1, wherein the rim further comprises a corner and the fastener is configured to conform to the corner.
 13. A system according to claim 1, wherein the clamping rail is further configured to reduce electromagnetic interference passing between the cover and the rim.
 14. A method for clamping a cover having a first surface onto a vehicular chassis body having a rim, the rim having a second surface, the method comprising the steps of: circumferentially aligning a clamping loop to the first and second surfaces; constricting the circumference of the clamping loop to engage the first and second surfaces with a first force substantially coplanar with the loop, the clamping loop and the first and second surfaces being configured to convert at least a portion of the first force to a second force substantially orthogonal to the loop that clamps the cover onto the rim; and fixing the clamping loop in its circumferentially restricted position.
 15. The method of claim 14, further comprising the step of inserting a seal between the cover and the rim.
 16. The method of claim 14, wherein the clamping loop further comprises a first end and a second end and the step of fixing the clamping loop further comprises fixing the clamping loop by welding the first and second ends together.
 17. A system for clamping a cover onto a rim of a vehicular chassis, the cover having a first surface residing in a first plane, and the rim having a second surface residing in a second plane, the system comprising: a clamping rail circumscribing the first and second surfaces, the clamping rail comprising: a first arm configured to engage the first surface and residing in a third plane; and a second arm configured to engage the second surface and residing in a fourth plane, the rail generating a clamping force that clamps the cover to the rim when the rail is constricted and at least one of the first plane and the second plane is different than the third plane and the fourth plane, respectively; and a fastener coupled to the rail configured to constrict the rail.
 18. A system according to claim 17, wherein the chassis further comprises a corner, and the first and second arms are notched proximate to the corner. 